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The following image shows how this works. The top panel of the IGB main display window shows the normal, non-spliced view of a region containing overlapping genes from a cow, GBN4, which contains an enormous five prime intron human, AGBL4 which contains several very large introns, one of which that completely encompasses another gene, ZNF639, which encodes a zinc finger proteinBEND5. The Sliced View panel on the bottom shows these same two genesAGBL4, and then BEND5, but with the intronic sequences reduced to 100bp. The places points where the slices introns were made shortened appear as black hash marks below in the coordinate axis in of the Sliced View tab. Note how the sliced view makes it easy to see both the gene structures simultaneously, whereas in the main view ZNF639 is the exons of AGBL4 are so small it is impossible to even see size comparisons of the number of exons it contains. 
You can enter the size you want the introns to be set at by changing the number in the Slice Buffer (default is 100). By unchecking the Slice by Selection box, you can move the main view to another region of interest, and click on other features without changing the sliced view.
Another feature that the Sliced View panel supports is finding open reading frames (ORFs) and stop codons. For details on using this function, please see Additional and Alternate Views of Annotationssee Changing the Appearance of Tracks.